The invention relates to seal assemblies for rotating shafts the oil lubricated bearings of which have to be protected against a liquid medium such as water. In preferred embodiments the invention relates to the outboard end of a sealing of the aft end of the stern tube bearing of a ship.
In the prior art a stern seal assembly is known in which a mechanical seal comprising a slide ring is used as seal between a void space and the sea-water surrounding the propeller shaft of a ship. The mechanical seal does not prevent sufficiently the sea-water to penetrate through the seal into the space and to bring in sand and other abrasive particles which create wear.
Recently it was proposed to protect the slide ring of a water seal against abrasion by providing a seal assembly with an annular space at the outboard end of the slide ring. The annular space was filled with a liquid medium not polluting the sea-water and was sealed against the sea-water by a lip seal through which the liquid medium could leak out thereby cleaning the lip seal. However, this structure showed some disadvantages e.g. because of differences in pressure of the sea-water and the insufficiencies of a lip seal.